Relationship between the Modes of Winter Tropical Pacific SST Anomalies and the Intraseasonal Variations of the Following Summer Rainfall Anomalies in China

In present study,EOF analysis and extended singular value decomposition (ESVD) analysis are performed to explore the relationship between the winter tropical sea surface temperature anomalies (SSTAs) in the Pacific and the following summer rainfall anomalies in China.The two leading modes of winter tropical SSTAs in the Pacific are the SSTAs pattern characterized by "positive anomalies in the East and negative anomalies in the West" like the typical eastern Pacific El Nio and negative anomalies in the West and the central Pacific warming pattern characterized by "positive anomalies in the central region but negative anomalies in the East and West".The intraseasonal variations of the rainfall anomalies during the following summer in China that are associated with the eastern Pacific warming mode are characterized by positive anomalies south of the Yangtze River and negative anomalies in the Yangtze-Huai River Valley in June,and negative anomalies in South China and positive anomalies in the Yangtze River Valley and North China in July and August.In contrast,after the central Pacific warming mode,the corresponding intraseasonal variations of China’s summer rainfall are characterized by a nearly consistent pattern during the three summer months,which is positive in the South China coast and North China and negative in the Yangtze River Valley except for the positive anomalies in the Yangtze-Huai River Valley in July.These results may provide a reference for the seasonal prediction of the summer drought and flood distributions in China.

The Combined Effects of the Tropical and Extratropical Quasi-biweekly Oscillations on the Record-setting Mei-yu Rainfall in the Summer of 2020

During June-July 2020,the strongest recorded mei-yu rainfall occurred in the middle and lower reaches of the Yangtze River.The rainfall processes exhibited an obvious quasi-biweekly(biweekly in brief)variability,and there are altogether five cycles.It is found that the biweekly rainfall cycle mainly arises from the collaborative effects of biweekly variabilities from both the tropics and extratropics.As for the tropics,the biweekly meridional march and retreat of the western Pacific subtropical high(WPSH)is particularly evident.As for the extratropics,geopotential height anomalies near Lake Baikal are active.The former is attributed to the intensified biweekly activity of the southwest-northeast oriented EastAsian Pacific wave train(EAP)originating from the tropical western Pacific,while the latter is associated with the biweekly activities of the eastward propagating Eurasia mid-high latitudinal wave train and the westward propagating North Pacific wave train.Why the biweekly activities of these wave trains intensified is further diagnosed from the perspective of thermodynamical forcing and also from the modulation of interannual background on intraseasonal variability.It is found that the strongest recorded convection anchoring over the tropical western Indian Ocean(IO)triggers anomalous descent over the tropical western Pacific,which modulates the biweekly activity of the EAP.Meanwhile,the anomalous diabatic heating over the IO causes changes of the meridional thermodynamic contrast across the IO to the high latitudes,which modulates the extratropical wave trains.A further diagnosis of barotropic kinetic energy conversion suggests that the active occurrence of two extratropical biweekly wave trains is attributed to the increased efficiency of energy conversion from basic flow.The westward propagation of the extratropical North Pacific wave train is attributed to the weakened and northshifted upper-level westerly,which is caused by the SST warmth near the Kuroshio extension.